Magnetic random access memory

ABSTRACT

A magnetic random access memory according to the present invention is provided with: a magnetic recording layer including a magnetization free region having a reversible magnetization, wherein a write current is flown through the magnetic recording layer in an in-plane direction; a magnetization fixed layer having a fixed magnetization; a non-magnetic layer provided between the magnetization free region and the magnetization fixed layer; and a heat sink structure provided to be opposed to the magnetic recording layer and having a function of receiving and radiating heat generated in the magnetic recording layer. The magnetic random access memory thus-structured radiates heat generated in the magnetic recording layer by using the heat sink structure, suppressing the temperature increase caused by the write current flown in the in-plane direction.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of co-pending application Ser. No.12/297,153 filed on Oct. 14, 2008, which is a National Stage ofPCT/JP2007/057839 filed on Apr. 9, 2007, which claims foreign priorityto Japanese Application No. 2006-108480 filed on Apr. 11, 2006. Theentire content of each of these applications is hereby expresslyincorporated by reference.

TECHNICAL FIELD

The present invention relates to an MRAM (magnetic random accessmemory), and more particularly relates to an MRAM in which aspin-polarized current is used to invert the magnetization to writedata.

BACKGROUND ART

One of the promising methods for data writing in MRAMs proposed inrecent years is the spin momentum transfer, which involves injecting aspin-polarized current as a write current into a magnetic recordinglayer and consequently inverting the magnetization of the magneticrecording layer. The spin momentum transfer allows decreasing thenecessary current with the reduction of the size of the memory cell,while the magnetization inversion by using the current magnetic field isaccompanied by an increase in the necessary current with the decrease inthe size of a memory cell. Thus, the spin momentum transfer isconsidered as a promising method to realize an MRAM with an increasedcapacity.

However, the use of spin momentum transfer for a magnetic tunneljunction device requires overcoming the problem of the tunnel barrierlayer breakdown. In the current technique, the spin-polarized current ofseveral mA or more is required to be injected into the magneticrecording layer, when spin momentum transfer is used to invert themagnetization. However, feeding such a large current through themagnetic tunnel junction may result in the breakdown of the tunnelbarrier layer.

One approach for overcoming the problem of the tunnel barrier layerbreakdown is a technique that feeds a spin-polarized current in thein-plane direction of the magnetic recording layer to causemagnetization inversion. Such techniques are disclosed in, for example,Japanese Laid Open Patent Application (P2005-191032A), Japanese LaidOpen Patent Application (P2005-123617A), and U.S. Pat. No. 6,781,871.Feeding a spin-polarized current in the in-plane direction of themagnetic recording layer allows moving the magnetic wall of the magneticrecording layer and/or exerting a torque on the magnetization of themagnetic recording layer by the spin-polarized current, consequentlyinverting the magnetization of the magnetic recording layer. Thetechnique which feeds a spin-polarized current in the in-plane directionof the magnetic recording layer eliminates the need for flowing thespin-polarized current through the tunnel barrier layer, effectivelyavoiding the problem of the breakdown of the tunnel barrier layer.

According to a study of the inventor, one issue of the MRAM in which aspin-polarized current is flown in the in-plane direction of themagnetic recording layer is the heat generation in the magneticrecording layer. The resistance of the magnetic recording layer isinevitably high in the in-plane direction, since ferromagnetic materialhas a high electric resistivity in general. On the other hand, theinversion of the magnetization of the magnetic recording layer requiresa high spin-polarized current to some extent. Therefore, feeding thespin-polarized current in the in-plane direction of the magneticrecording layer for data write increases the temperature of the memorycell. The temperature increase in the memory cell undesirably causes thedrop in the reliability of the MRAM operation. It is desired to providea technique for suppressing the temperature increase caused by the writecurrent flowing in the in-plane direction of the magnetic recordinglayer.

DISCLOSURE OF INVENTION

It is therefore an object of the present invention to provide atechnique for suppressing the temperature increase caused by the writecurrent flowing in the in-plane direction of the magnetic recordinglayer.

In one aspect of the present invention, a magnetic random access memoryis provided with a magnetic recording layer including a magnetizationfree region having a reversible magnetization, through which layer awrite current is flown in an in-plane direction; a magnetization fixedlayer having a fixed magnetization; a non-magnetic layer providedbetween the magnetization free region and the magnetization fixed layer;and a heat sink structure provided to be opposed to the magneticrecording layer and having a function of receiving and radiating heatgenerated in the magnetic recording layer. The magnetic random accessmemory thus-structured radiates heat generated in the magnetic recordinglayer by using the heat sink structure, suppressing the temperatureincrease caused by the write current flown in the in-plane direction.

In one embodiment, the magnetic recording layer further includes a firstmagnetization fixed region coupled with a first boundary of saidmagnetization free region and a second magnetization fixed regioncoupled with a second boundary of said magnetization free region. Inthis case, the write current is flown from said first magnetizationfixed region to the second magnetization fixed region or from the secondmagnetization fixed region to the first magnetization fixed region.

To improve the heat radiation efficiency, it is preferable that the heatsink structure is directly coupled with said magnetic recording layer.

In one embodiment, the magnetic random access memory further includes afirst interconnection electrically connected with the firstmagnetization fixed region; and a second interconnection electricallyconnected with the second magnetization fixed region. In this case, theheat sink structure is preferably provided between the firstmagnetization fixed region and the first interconnection.

In the case where the magnetic random access memory further includes avia contact providing a connection between the second magnetizationfixed region and the second interconnection, it is preferable that theheat sink structure is provided with an opening, and the via contact isprovided through said opening.

The magnetic random access memory is preferably provided with anotherheat sink structure provided between the second magnetization fixedregion and the second interconnection so as to be opposed to themagnetic recording layer and having a function of receiving andradiating heat generated in said magnetic recording layer.

In this case, it is preferable that the heat sink structure is directlycoupled with the first magnetization fixed region, and the other heatsink structure is directly coupled with the second magnetization fixedregion.

When the magnetic random access memory further includes a thirdinterconnection electrically connected to the magnetization fixed layer,the heat sink structure may be provided between the thirdinterconnection and the magnetization fixed layer. In this case, it ispreferable that the heat sink structure is directly coupled with themagnetization fixed layer. In this case, the heat sink structure ispreferably provided within a via contact layer just below aninterconnection layer within which the third interconnection isprovided.

In another embodiment, it is preferable that the third interconnectionfunctions as the heat sink structure by including an interconnectionmain body extending in a first direction in which a read current isflown and a protrusion protruding from the interconnection main body ina second direction vertical to the first direction.

In another embodiment, it is preferable that a first interconnectionelectrically connected with the first magnetization fixed region,through which interconnection the write current is flown, functions asthe heat sink structure by including an interconnection main bodyextending in a first direction in which the write current is flown and aprotrusion protruding from the interconnection main body in a seconddirection vertical to the first direction.

The heat sink structure may be positioned within the sameinterconnection layer as a first interconnection electrically connectedwith the first magnetization fixed region and a second interconnectionelectrically connected with the second magnetization fixed region.

The heat sink structure may be positioned within the sameinterconnection layer as a third interconnection electrically connectedwith the magnetization fixed layer.

In another aspect of the present invention, a magnetic random accessmemory is provided with a magnetic recording layer including amagnetization free region having a reversible magnetization, a firstmagnetization fixed region connected to a first boundary of themagnetization free region, and a second magnetization fixed regionconnected to a second boundary of the magnetization free region, throughwhich layer a write current is flown in an in-plane direction; amagnetization fixed layer having a fixed magnetization; a non-magneticlayer provided between the magnetization free region and themagnetization fixed layer; and a first interconnection electricallyconnected to the first magnetization fixed region. The write current isflown from the first magnetization fixed region to the secondmagnetization fixed region or from the second magnetization fixed regionto the first magnetization fixed region. The first interconnectionincludes: an interconnection main body extending in a first direction inwhich the write current is flown; and a protrusion protruding from theinterconnection main body in a second direction vertical to the firstdirection, the protrusion being opposed to the magnetic recording layer.

In the magnetic random access memory thus-structured, the firstinterconnection, which includes the protrusion, functions as a heat sinkstructure that radiates heat generated in the magnetic recording layer,suppressing the temperature increase caused by the write current flownin the in-plane direction.

In still another aspect of the present invention, a magnetic randomaccess memory is provided with: a magnetic recording layer including amagnetization free region having a reversible magnetization, throughwhich layer a write current is flown in an in-plane direction; amagnetization fixed layer having a fixed magnetization; a non-magneticlayer provided between the magnetization free region and themagnetization fixed region; and a third interconnection electricallyconnected to the magnetization fixed layer. The third interconnectionincludes: an interconnection main body extending in a first direction inwhich a read current is flown; and a protrusion protruding from theinterconnection main body in a second direction vertical to the firstdirection, the protrusion being opposed to the magnetic recording layer.

In the magnetic random access memory thus-structured, the thirdinterconnection, which includes the protrusion, functions as a heat sinkstructure that radiates heat generated in the magnetic recording layer,suppressing the temperature increase caused by the write current flownin the in-plane direction.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a sectional view showing the structure of an MRAM in oneexemplary embodiment of the present invention;

FIG. 1B is a conceptual view explaining the function of the MRAM in FIG.1A;

FIG. 2 is a plan view showing the structure of an MRAM in one exemplaryembodiment of the present invention;

FIG. 3 is a sectional view showing the structure of an MRAM in anotherexemplary embodiment of the present invention;

FIG. 4 is a sectional view showing the structure of an MRAM in stillanother exemplary embodiment of the present invention;

FIG. 5A is a perspective view showing the structure of an MRAM in afirst example;

FIG. 5B is a plan view showing the structure of the MRAM in the firstexample;

FIG. 6A is a perspective view showing the structure of an MRAM in asecond example;

FIG. 6B is a plan view showing the structure of the MRAM in the secondexample;

FIG. 7A is a perspective view showing the structure of an MRAM in athird example;

FIG. 7B is a plan view showing the structure of the MRAM in the thirdexample;

FIG. 8A is a perspective view showing the structure of an MRAM in afourth example;

FIG. 8B is a perspective view showing another structure of the MRAM inthe fourth example;

FIG. 9A is a perspective view showing the structure of an MRAM in afifth example;

FIG. 9B is a perspective view showing another structure of the MRAM inthe fifth example;

FIG. 9C is a perspective view showing still another structure of theMRAM in the fifth example;

FIG. 10A is a perspective view showing the structure of an MRAM in asixth example;

FIG. 10B is a plan view showing the structure of the MRAM in the sixthexample;

FIG. 11A is a perspective view showing the structure of an MRAM in aseventh example;

FIG. 11B is a plan view showing the structure of the MRAM in the seventhexample;

FIG. 12A is a perspective view showing the structure of an MRAM in aneighth example;

FIG. 12B is a plan view showing the structure of the MRAM in the eighthexample;

FIG. 13A is an perspective view showing the structure of an MRAM in aninth example; and

FIG. 13B is a plan view showing the structure of the MRAM in the ninthexample.

BEST MODES FOR CARRYING OUT THE INVENTION

In the following, various exemplary embodiments of the present inventionwill be described below with reference to the attached drawings. Itshould be noted that same or corresponding numerals denote same orsimilar elements in the drawings.

FIG. 1A is a sectional view showing the schematic structure of an MRAMin one exemplary embodiment of the present invention. In an MRAM in oneexemplary embodiment of the present invention, a memory cell 1 is formedwithin a dielectric layer 10. The memory cell 1 is provided with amagnetic recording layer 2, a tunnel barrier layer 3 and a magnetizationfixed layer 4.

The magnetic recording layer 2 is provided with a magnetization freeregion 5 and magnetization fixed regions 6 and 7, as shown in FIG. 2.The magnetization free region 5 is a region in which one-bit data isstored as the direction of the magnetization thereof. The magnetizationfree region 5 is shaped to be long in the x-axis direction, and themagnetization of the magnetization free region 5 is oriented in parallelto the x-axis direction. The magnetization free region 5 is formed ofmagnetically soft ferromagnetic material, and the magnetization of themagnetization free region 5 is reversible. In this exemplary embodiment,the state in which the direction of the magnetization of themagnetization free region 5 is the +x direction is associated with data“1”, and the state in which the direction of the magnetization of themagnetization free region 5 is the −x direction is associated with data0”.

The magnetization fixed regions 6 and 7 are regions used to inject aspin-polarized current into the magnetization free region 5 in thein-plane direction, both formed of ferromagnetic material. Themagnetization fixed region 6 is coupled with the magnetization freeregion 5 on the boundary 8 at one end of the magnetization free region5, and the magnetization fixed region 7 is coupled with themagnetization free region 5 in the boundary 9 at the other end of themagnetization free region 5. The magnetization fixed regions 6 and 7 areadjacent to the magnetization free region 5 in the x-axis direction andshaped to be long in the x-axis direction. The magnetization directionsof the magnetization fixed regions 6 and 7 are both fixed in thedirections toward the magnetization free region 5. Specifically, themagnetization of the magnetization fixed region 6 is fixed in the +xdirection, and the magnetization of the magnetization fixed region 7 isfixed in the −x direction. Instead, the magnetization directions of themagnetization fixed regions 6 and 7 may be both fixed in the directionsaway from the magnetization free region 5. In this case, themagnetization of the magnetization fixed region 6 is fixed in the −xdirection, and the magnetization of the magnetization fixed region 7 isfixed in the +x direction.

Referring back to FIG. 1A, the tunnel barrier layer 3 is a thinnon-magnetic dielectric layer through which a tunnel current flowsbetween the magnetization fixed layer 4 and the magnetization freeregion 5. The tunnel barrier layer 3 is formed of, for example, aluminumoxide (AlO_(x)) or magnesium oxide (MgO).

The magnetization fixed layer 4 is a ferromagnetic layer having a fixedmagnetization. The magnetization fixed layer 4 is formed of magneticallyhard ferromagnetic material, such as CoFe. As shown in FIG. 2, themagnetization fixed layer 4 is shaped to be long in the x-axisdirection, and the magnetization of the magnetization fixed layer 4 isoriented in the −x direction. The magnetization free region 5 of themagnetic recording layer 2, the tunnel barrier layer 3 and themagnetization fixed layer 4 configure a magnetic tunnel junction (MTJ)which exhibits the TMR effect, and the resistance of the magnetic tunneljunction depends on the relative direction between the magnetizations ofthe magnetization fixed layer 4 and the magnetization free region 5.

The TMR effect is used to read data stored in the magnetization freeregion 5. The resistance of the magnetic tunnel junction, which includesthe tunnel barrier layer 3 and the magnetization fixed layer 4, dependson the relative direction between the magnetizations of themagnetization fixed layer 4 and the magnetization free region 5, due tothe TMR effect. When the magnetizations of the magnetization fixed layer4 and the magnetization free region 5 are anti-parallel, the magnetictunnel junction exhibits a relatively high resistance, and when themagnetizations of the magnetization fixed layer 4 and the magnetizationfree region 5 are parallel, the magnetic tunnel junction exhibits arelatively low resistance. The data stored in the magnetic recordinglayer 2 is identified by detecting the change in the resistance of themagnetic tunnel junction. The change in the resistance of the magnetictunnel junction can be identified by applying a predetermined voltage tothe magnetic tunnel junction and measuring the current flowing throughthe magnetic tunnel junction, or by feeding a predetermined current tothe magnetic tunnel junction and measuring the voltage generated acrossthe magnetic tunnel junction.

The data writing into the magnetization free region 5 is carried out byinjecting a spin-polarized current into the magnetization free region 5from the magnetization fixed region 6 or 7. To write data “1”, a currentis flown in the +x direction through the magnetic recording layer 2.This allows injecting a spin-polarized current into the magnetizationfree region 5 from the magnetization fixed region 6 (which has amagnetization fixed in the +x direction). The injected spin-polarizedcurrent pushes the magnetic wall of the magnetization free region 5 inthe +x direction, or applies a torque to the magnetization, and therebyorients the magnetization of the magnetization free region 5 in the +xdirection. This achieves writing data “1” onto the magnetic recordinglayer. To write data “0”, on the other hand, a spin-polarized current isinjected into the magnetization free region 5 from the magnetizationfixed region 7 (which has a magnetization fixed in the −x direction).This allows orienting the magnetization of the magnetization free region5 in the −x direction.

The MRAM in one exemplary embodiment of the present inventionadditionally includes heat sink structures 11 and 12. The heat sinkstructure 11 is formed to be opposed to the bottom surface of themagnetic recording layer 2, and the heat sink structure 12 is formed tobe opposed to the top surface of the magnetic recording layer 2. Theheat sink structures 11 and 12 are formed of material with a highthermal conductivity, more specifically, metal such as copper, aluminumand tungsten, and the heat sink structures 11 and 12 are dedicated toreceive and radiate the heat generated in the magnetic recording layer2. As shown in FIG. 1B, the magnetic recording layer 2, which is formedof ferromagnetic material, suffers from a problem of the heat generationin the magnetic recording layer 2 due to the inevitably high resistancethereof, when a spin-polarized current is fed in write operations. Asshown in FIG. 1B, the heat sink structures 11 and 12 function as heatsinks for radiating the heat generated in the magnetic recording layer 2and effectively suppresses the temperature increase in the magneticrecording layer 2. Although the MRAM in FIG. 1A is provided with theheat sink structures 11 and 12, opposed to the top and bottom surfacesof the magnetic recording layer 2, respectively, only one of the heatsink structures 11 and 12 may be provided.

As shown in FIG. 3, the heat sink structure 11 may be directly coupledwith the bottom surface of the magnetic recording layer 2. The directcontact of the heat sink structure 11 with the magnetic recording layer2 preferably improves the heat radiation efficiency. In the same way,the heat sink structure 12 may be directly coupled with themagnetization fixed layer 4.

The geometrical arrangement of the magnetization free region 5 and themagnetization fixed regions 6 and 7 in the magnetic recording layer 2 isnot limited to the arrangement in which the magnetization free region 5and the magnetization fixed regions 6 and 7 are aligned in a straightline. For example, as shown in FIG. 4, the magnetization free region 5may be formed to be long in the x-axis direction, and the magnetizationfixed regions 6 and 7 may be formed long in the y-axis direction. Inthis case, the magnetizations of the magnetization fixed regions 6 and 7are both fixed in the +y direction. Instead, the magnetizations of themagnetization fixed regions 6 and 7 may be both fixed in the −ydirection.

In the following, a description is given of specific examples of thepresent invention.

First Example

FIG. 5A is a perspective view showing the structure of an MRAM in afirst example. Similarly to the MRAM in FIG. 1A, a memory cell 1 isprovided with a magnetic recording layer 2, a tunnel barrier layer 3 anda magnetization fixed layer 4. The magnetization fixed layer 4 isconnected to an upper interconnection 21 for feeding a read currentI_(R) through a via contact 19. The upper interconnection 21 is disposedto extend in the y-axis direction. This implies that the read currentI_(R) flows in the y-axis direction.

In the first example, the heat sink structure 11 is formed in the memorycell 1 between the magnetic recording layer 2 and lower interconnections15 and 18 through which write currents IW₁ and IW₂ are flown. The lowerinterconnections 15 and 18 are both disposed to extend in the y-axisdirection. The heat sink structure 11 is connected to the lowerinterconnection 15 through a via contact 14 and also connected to themagnetization fixed region 6 of the magnetic recording layer 2 through avia contact 13. The lower interconnection 18 is connected through a viacontact 16 to the magnetization fixed region 7 of the magnetic recordinglayer 2. The via contact 16 is formed through an opening 11 a providedthrough the heat sink structure 11, and electrically isolated from theheat sink structure 11.

In the MRAM such structured, a voltage is applied between the upperinterconnection 21 and the lower interconnection 15 (or between theupper interconnection 21 and the lower interconnection 18) in a readoperation to flow a read current I_(R) from the upper interconnection 21to the lower interconnection 15 through the memory cell 1. The datastored in the magnetization free region 5 of the magnetic recordinglayer 2 is identified from the current level of the read current I_(R).In a write operation, on the other hand, a write current IW₁ is fed fromthe lower interconnection 15 to the lower interconnection 18, or a writecurrent IW₂ is fed from the lower interconnection 18 to the lowerinterconnection 15, depending on data to be written. When the writecurrent IW₁ is fed from the lower interconnection 15 to the lowerinterconnection 18, the spin-polarized current is injected into themagnetization free region 5 from the magnetization fixed region 6, andthe magnetization of the magnetization free region 5 is oriented in the+x direction. That is, data “1” are written onto the magnetic recordinglayer. On the other hand, when the write current IW₂ is flown from thelower interconnection 18 to the lower interconnection 15, thespin-polarized current is injected into the magnetization free region 5from the magnetization fixed region 7 and the magnetization of themagnetization free region 5 is oriented in the −x direction. That is,data “0” are written onto the magnetic recording layer.

It is preferable that the heat sink structure 11 is arranged in a shapeand arrangement which maximize the area opposed to the magneticrecording layer 2. FIG. 5B is a plan view showing a preferred shape andarrangement of the heat sink structure 11. Preferably, the heat sinkstructure 11 is formed to be opposed at least to the whole of themagnetization free region 5 and magnetization fixed region 6 of themagnetic recording layer 2. Such arrangement increases the area opposedto the magnetic recording layer 2, and effectively improves the heatdissipation efficiency of the heat sink structure 11. In order tofurther increase the area at which the heat sink structure 11 is opposedto the magnetic recording layer 2, the heat sink structure 11 ispreferably formed to be opposed to the whole of the magnetic recordinglayer 2, except the portion opposed to the opening 11 a formed throughthe heat sink structure 11. FIG. 5B shows an arrangement of the heatsink structure 11 in which the heat sink structure 11 is formed to beopposed to the whole of the magnetic recording layer 2, except theportion opposed to the opening 11 a formed through the heat sinkstructure 11.

Second Example

FIG. 6A is a perspective view showing the structure of an MRAM in asecond example. In the second example, two heat sink structures 11A and11B are formed between the magnetic recording layer 2 and the lowerinterconnections 15 and 18. The heat sink structure 11A is connected tothe magnetization fixed region 6 of the magnetic recording layer 2through a via contact 13 and also connected through a via contact 14 tothe lower interconnection 15. On the other hand, the heat sink structure11B is connected through a via contact 16 to the magnetization fixedregion 7 of the magnetic recording layer 2 and also connected throughthe via contact 17 to the lower interconnection 18. Read and writeoperations in the such-structured MRAM of the second example areperformed similarly to those in the MRAM of the first example.

Preferably, the heat sink structures 11A and 11B are arranged in a shapeand arrangement which maximize the area opposed to the magneticrecording layer 2. FIG. 6B is a plan view showing a preferable structureand arrangement for the heat sink structures 11A and 11B. Preferably,the heat sink structure 11A is formed to be opposed at least to thewhole of the magnetization free region 6 of the magnetic recording layer2. Preferably, the heat sink structure 11B is formed to be opposed tothe whole of the magnetization fixed region 7 of the magnetic recordinglayer 2. Such arrangement increases the area at which the heat sinkstructures 11A and 11B are opposed to the magnetic recording layer 2 andeffectively improves the heat radiation efficiency.

It is further preferable for further increasing the area opposed to themagnetic recording layer 2 that the heat sink structures 11A and 11B areformed to be opposed to at least a portion of the magnetization freeregion 5 of the magnetic recording layer 2; it is further preferablethat the heat sink structures 11A and 11B are arranged to be opposed toat least a portion of the bottom surface of the magnetization fixedlayer 4 (that is, the face coupled with the tunnel barrier layer 3).FIG. 6B shows an arrangement in which the heat sink structures 11A and11B are each opposed to portions of the bottom surface of themagnetization fixed layer 4. It is preferable that the heat sinkstructures 11A and 11B are spaced by a narrow spacing; it is mostpreferable that the heat sink structures 11A and 11B are spaced by thesame interval as the minimal pitch of the design rule of the MRAM.

Third Example

FIG. 7A is a perspective view showing the structure of an MRAM in athird example. In the third example, a heat sink structure 12 is formedbetween the magnetization fixed layer 4 and the upper interconnection 21in the memory cell 1. The heat sink structure 12 is connected to themagnetization fixed layer 4 through a via contact 19 and also connectedto the upper interconnection 21 through a via contact 20. In thesuch-structured MRAM in the third example, read and write operations areexecuted similarly to those in the MRAM of the first example.

Preferably, the heat sink structure 12 is arranged in a shape andarrangement which maximize the area opposed to the magnetic recordinglayer 2. FIG. 7B is a plan view showing a preferable structure andarrangement for the heat sink structure 12. Preferably, the heat sinkstructure 12 is formed to be opposed at least to the whole of theportion of the magnetic recording layer 2 between the via contacts 13and 16. Such arrangement allows the heat radiation from the whole of theheat generating portion of the magnetic recording layer 2 (namely, theportion through which the spin-polarized current flows). For furtherimproving the heat dissipation efficiency, it is further preferable thatthe heat sink structure 12 is formed to be opposed to the whole of themagnetic recording layer 2. Such arrangement increases the area opposedto the magnetic recording layer 2 and effectively improves the heatdissipation efficiency of the heat sink structure 12.

Fourth Example

FIG. 8A is a perspective view showing the structure of an MRAM in afourth example. In the MRAM of the fourth example, the heat sinkstructure 11 is directly coupled with the whole of the bottom surface ofthe magnetic recording layer 2. The heat sink structure 11 is connectedto the lower interconnection 15 through the via contact 14 and furtherconnected to the lower interconnection 18 through a via contact 17. Theheat sink structure 11 is formed of material having a resistivity higherthan that of the magnetic recording layer 2. This is important forfeeding a larger current to the magnetic recording layer 2. Although thewrite current is branched into the heat sink structure 11 in the MRAMshown in FIG. 8A, a reduced current is flown through the heat sinkstructure 11, since the heat sink structure 11 is formed of materialhaving a resistivity higher than that of the magnetic recording layer 2.On the other hand, the fact that the heat sink structure 11 is directlycoupled with the entire surface of the bottom surface of the magneticrecording layer 2 enhances the heat transmission from the magneticrecording layer 2 to the heat sink structure 11, and thereby improvesthe heat radiation efficiency. In the such-structured MRAM of the fourthexample, read and write operations are carried out similarly to those inthe MRAM in the first example.

FIG. 8B is a perspective view showing another structure of the MRAM inthe fourth example. In the MRAM of the fourth example, two heat sinkstructures 11A and 11B are directly coupled with the bottom surface ofthe magnetic recording layer 2. The heat sink structure 11A is directlycoupled with the magnetization fixed region 6 of the magnetic recordinglayer 2 and also connected through the via contact 14 to the lowerinterconnection 15. On the other hand, the heat sink structure 11B isdirectly coupled with the magnetization fixed region 7 of the magneticrecording layer 2 and also connected to the lower interconnection 18through the via contact 17. The fact that the two heat sink structures11A and 11B are directly coupled with the bottom surface of the magneticrecording layer 2 enhances the heat transmission from the magneticrecording layer 2 to the heat sink structures 11A and 11B, andeffectively improves the heat radiation efficiency. On the other hand,the current through the heat sink structure 11 (not through the magneticrecording layer 2) is reduced, since the heat sink structures 11A and11B are electrically isolated. In the such-structured MRAM of the fourthexample, read and write operations are carried out similarly to those inthe MRAM in the first example.

Preferably, the width of the heat sink structure 11A in the x-axisdirection (namely, the width in the direction vertical to the directionin which the lower interconnection 15 extends) is larger than that ofthe lower interconnection 15 through which the write current IW₁ flows.Such structure enhances the heat transmission from the magneticrecording layer 2 to the heat sink structures 11A and 11B, effectivelyimproving the heat radiation efficiency. In the same way, it ispreferable that the width of the heat sink structure 11B in the x-axisdirection (namely, the width in the direction vertical to the directionin which the lower interconnection 18 extends) is larger than that ofthe lower interconnection 18 through which the write current IW₂ flows.

Fifth Example

FIG. 9A is a perspective view showing the structure of an MRAM in afifth example. In the MRAM of the fifth example, the heat sink structure12 is directly coupled with the magnetization fixed layer 4. The heatsink structure 12 is formed within a via-contact layer located justbelow the interconnection layer within which the upper interconnection21 is laid. The heat sink structure 12 is directly coupled with theupper interconnection 21. The heat sink structure 12 is mainly formed ofcopper (Cu) or tungsten (W). The structure in which the heat sinkstructure 12 is formed within the via contact layer located just underthe interconnection layer within which the upper interconnection 21 isprovided is preferable, because the step of producing the heat sinkstructure 12 is not additionally required. In the such-structured MRAMof the fifth example, read and write operations are carried outsimilarly to those in the MRAM in the first example.

Preferably, the width of the heat sink structure 12 in the x-axisdirection (namely, the width in the direction vertical to the directionin which the lower interconnection 15 extends) is larger than that ofthe lower interconnection 15 through which the read current I_(R) flows.Such structure enhances the heat transmission from the magneticrecording layer 2 to the heat sink structure 12, effectively improvingthe heat radiation efficiency.

It is also preferable that the thickness d₂ of the heat sink structure12 is thicker than the thickness d₁ of the magnetic recording layer 2.Such structure effectively improves the heat radiation efficiency.

As shown in FIGS. 9B and 9C, the heat sink structure 12 is not requiredto be perfectly aligned to the magnetization fixed layer 4. As shown inFIG. 9B, the heat sink structure 12 may be formed to be coupled withonly a portion of the magnetization fixed layer 4. Also, as shown inFIG. 9C, the heat sink structure 12 may be coupled with the whole of thetop surface of the magnetization fixed layer 4 and arranged to protrudefrom the magnetization fixed layer 4.

Sixth Example

FIG. 10A is a perspective view showing the structure of an MRAM in asixth example. In the MRAM of the sixth example, the upperinterconnection 21 is shaped to function as a heat sink structure. Thatis, the upper interconnection 21 is provided with protrusions 21 a whichprotrude in the directions (the x-axis directions for the sixth example)vertical to the extension direction (the y-axis direction in the sixthfor the sixth example). The protrusions 21 a are shaped to be opposed tothe top surface of the magnetic recording layer 2. The such-shaped upperinterconnection 21 effectively functions as a heat sink structure andeffectively radiates the heat generated in the magnetic recording layer2. The structure in which the upper interconnection 21 functions as theheat sink structure does not require an interconnection layer dedicatedfor forming the heat sink structure, allowing the MRAM to bemanufactured with a reduced number of interconnection layers. In thesuch-structured MRAM of the sixth example, read and write operations arecarried out similarly to those in the MRAM of the first example.

Preferably, the upper interconnection 21 is arranged in a shape andarrangement which maximize the area opposed to the magnetic recordinglayer 2. FIG. 10B is a plan view showing a preferred shape of the upperinterconnection 21. An interconnection main body 21 b of the upperinterconnection 21 is formed to extend in the y-axis direction (thedirection in which the read current I_(R) flows), and the protrusions 21a are formed to protrude in the x-axis directions from the wiring mainbody 21 b. Preferably, the protrusions 21 a are formed such that theupper interconnection 21 is shaped to be opposed at least to the wholeof the portion between the via contacts 13 and 16 of the magneticrecording layer 2. Such arrangement enables the heat radiation from thewhole of the heat generating portion of the magnetic recording layer 2(namely, the portion through which the spin-polarized current flows).For further improving the heat radiation efficiency, it is preferablethat the upper interconnection 21 is provided opposed to the whole ofthe magnetic recording layer 2. Such arrangement increases the areaopposed to the magnetic recording layer 2 and effectively improves theheat radiation efficiency of the upper interconnection 21.

Seventh Example

FIG. 11A is a perspective view showing the structure of an MRAM in aseventh example. In the MRAM of the sixth example, the lowerinterconnections 15 and 18 are shaped to function as heat sinkstructures. That is, the lower interconnection 15 is provided with aprotrusion 15 a that protrudes in the direction (the x-axis direction inthe seventh example) vertical to the extension direction thereof (they-axis direction in the seventh example), and the lower interconnection18 is provided with a protrusion 18 a that protrudes in the directionvertical to the extension direction thereof. The protrusions 15 a and 18a are shaped to be opposed to the top surface of the magnetic recordinglayer 2. The lower interconnections 15 and 18 with such shapeseffectively function as heat sink structures, effectively radiating theheat generated in the magnetic recording layer 2. The structure in whichthe lower interconnections 15 and 18 function as the heat sinkstructures does not require an interconnection layer dedicated for theformation of the heat sink structures, allowing the manufacture of theMRAM with a reduced number of interconnection layers. In thesuch-structured MRAM of the seventh example, read and write operationsare carried out similarly to those of the MRAM in the first example.

Preferably, the lower interconnections 15 and 18 are arranged in a shapeand arrangement which maximize the area opposed to the magneticrecording layer 2. FIG. 11B is a plan view showing preferable shapes ofthe lower interconnections 15 and 18. An interconnection main body 15 bof the lower interconnection 15 is provided to extend in the y-axisdirection (the direction through which the write current IW₁ flows), andthe protrusion 15 a is formed to protrude in the x-axis direction fromthe interconnection main body 21 b. Similarly, an interconnection mainbody 18 b of the lower interconnection 18 is formed to extend in they-axis direction (the direction through which the write current IW₂flows), and the protrusion 18 a is formed to protrude in the x-axisdirection from the interconnection main body 18 b.

The protrusion 15 a is preferably formed so that the lowerinterconnection 15 is opposed at least to the whole of the magnetizationfixed region 6 of the magnetic recording layer 2 and the protrusion 18 ais preferably formed so that the lower interconnection 18 is opposed atleast to the whole of the magnetization fixed region 7 of the magneticrecording layer 2. Such arrangement increases the area in which thelower interconnections 15 and 18 are opposed to the magnetic recordinglayer 2 and effectively improves the heat radiation efficiency.

Preferably, the protrusions 15 a and 18 a are arranged so that the lowerinterconnections 15 and 18 are opposed to at least a portion of themagnetization free region 5 of the magnetic recording layer 2. It ismore preferable that the lower interconnections 15 and 18 are arrangedto be opposed to at least a portion of the bottom surface of themagnetization fixed layer 4 (the surface coupled with to the tunnelbarrier layer 3). FIG. 11B shows an arrangement in which the lowerinterconnections 15 and 18 are each opposed to a portion of the bottomsurface of the magnetization fixed layer 4. The protrusions 15 a and 18a are preferably spaced across a narrow spacing, and most preferably,the protrusions 15 a and 18 a are spaced by the same interval as theminimal pitch of the design rule of the MRAM.

Eighth Example

FIG. 12A is a perspective view showing the structure of an MRAM in aneighth example. In the MRAM of the eighth example, the heat sinkstructure 11, which is opposed to the bottom surface of the magneticrecording layer 2, is formed within the same interconnection layer asthe lower interconnections 15 and 18. The heat sink structure 11 isformed between the lower interconnections 15 and 18 and electricallyisolated from the lower interconnections 15 and 18. The structure inwhich the heat sink structure 11 is formed within the sameinterconnection layer as the lower interconnections 15 and 18 preferablyeliminates the need for the step for the formation of the heat sinkstructure.

Preferably, the heat sink structure 11 is arranged in a shape andarrangement that maximize the area opposed to the magnetic recordinglayer 2. For this purpose, as shown in FIG. 12B, it is preferable thatthe heat sink structure 11 is formed to traverse the magnetic recordinglayer 2.

In addition, in order to maximize the area opposed to the magneticrecording layer 2, it is preferable that the lower interconnection 15and the heat sink structure 11 are spaced by the same interval as theminimal pitch of the design rule of the MRAM. Correspondingly, it ispreferable that the lower interconnection 18 and the heat sink structure11 are spaced with separated at the same interval as the minimal pitchof the design rule of the MRAM.

Ninth Example

FIG. 13A is a perspective view showing the structure of an MRAM in aneighth example. In the MRAM in the eighth example, heat sink structures12A and 12B, which are opposed to the top surface of the magneticrecording layer 2, are formed within the same interconnection layer asthe upper interconnection 21. The heat sink structures 12A and 12B areelectrically isolated from the upper interconnection 21. The structurein which the heat sink structures 12A and 12B are formed within the sameinterconnection layer as the upper interconnection 21 preferablyeliminates the need for additional steps for the formation of the heatsink structures.

Preferably, the heat sink structures 12A and 12B are arranged in a shapeand arrangement that maximize the area opposed to the magnetic recordinglayer 2. In order to maximize the area opposed to the magnetic recordinglayer 2, as shown in FIG. 13B, it is preferable that the heat sinkstructures 12A and 12B are arranged to be opposed to at least a portionof the magnetization free region 5 in the magnetic recording layer 2; itis further preferable that the heat sink structures 12A and 12B arearranged to be opposed to at least a portion of the top surface of themagnetization fixed layer 4 (the surface coupled with the tunnel barrierlayer 3). FIG. 13B shows an arrangement in which the heat sinkstructures 12A and 12B are each opposed to a portion of the top surfaceof the magnetization fixed layer 4. It is preferable that the intervalbetween the upper interconnection 21 and the heat sink structure 12A isnarrow, and it is most preferable that the upper interconnection 21 andthe heat sink structure 12A are separated by the same interval as theminimal pitch of the design rule of the MRAM. Correspondingly, it ispreferable that the upper interconnection 21 and the heat sink structure12B are separated by the same interval as the minimal pitch of thedesign rule of the MRAM.

Although the first to ninth examples provide the MRAMs that includesonly one of a heat sink structure opposed to the top surface of themagnetic recording layer 2 and a heat sink structure opposed to thebottom surface thereof, it is preferable that the MRAM includes both ofthe heat sink structure opposite to the top surface of the magneticrecording layer 2 and the heat sink structure opposite to the bottomsurface, in order to further improve the heat radiation efficiency. Indetail, it is preferable that an MRAM adopts both of the arrangement ofthe heat sink structure shown in one of FIG. 5A, FIG. 6, FIG. 8, FIG.11A and FIG. 12A and the arrangement of the heat sink structure shown inone of FIG. 7A, FIG. 9A to FIG. 9C, FIG. 10A and FIG. 13A.

1. A magnetic random access memory comprising: a magnetic recordinglayer including a magnetization free region having a reversiblemagnetization, through which layer a write current is flown in anin-plane direction, said magnetic recording layer comprising: a firstmagnetization fixed region coupled with a first boundary of saidmagnetization free region and having a fixed magnetization; and a secondmagnetization fixed region coupled with a second boundary of saidmagnetization free region and having a fixed magnetization; amagnetization fixed layer having a fixed magnetization; a non-magneticlayer provided between said magnetization free region and saidmagnetization fixed layer; and a heat sink structure provided to beopposed to said magnetic recording layer and having a function ofreceiving and radiating heat generated in said magnetic recording layer;a first interconnection electrically connected with said firstmagnetization fixed region; and a second interconnection electricallyconnected with said second magnetization fixed region; wherein saidwrite current is flown from said first magnetization fixed region tosaid second magnetization fixed region or from said second magnetizationfixed region to said first magnetization fixed region; and wherein saidheat sink structure is positioned within the same interconnection layeras said first and second interconnections.